The present invention relates generally to an electronic apparatus that houses a circuit element, such as an LSI, and more particularly to a heat radiation structure for the circuit element that generates heat when it is operating. The present invention is suitable, for example, for heat radiations for LSI chips in a wide variety of packages, such as a ball grid array (“BGA”), a land grid array (“LGA”), and a pin grid array (“PGA”).
Along with recently widespread, small and sophisticated electronic apparatuses, a supply of an electronic apparatus that realizes high density mounting is increasingly demanded. In order to meet this demand, a BGA package is conventionally proposed. In general, the BGA package is one type of a package that is soldered to a printed board (also referred to as a “system board” or a “motherboard”), and is mounted with an IC or an LSI that generally serves as a CPU. The BGA package realizes a narrow pitch and multiple pins (many leads), and provides a sophisticated electronic apparatus through a higher density package.
As the CPU's performance improves, the heating value of the CPU increases and, in order to thermally protect the CPU, a cooling device called a heat sink is thermally connected to the CPU via a heat spreader. The heat sink includes cooling fins, stands close to the CPU, and radiates heat from the CPU through natural cooling.
FIG. 7 shows a schematic section of a conventional LSI chip 10 housed in a package. The LSI chip 10 includes transistors 12, each of which serves as an exoergic circuit element, and is mounted on a corresponding one of connectors 14 on a substrate 11. The connector 14 is connected to one or more signal wires (including a power supply wire) 16. Each signal wire 16 is connected to a corresponding one of bumps 18. The bump 18 is connected to an external board, and the transistor 12 is electrically connected to the external board via the signal wires 16 and the bumps 18. The substrate 11 contacts a heat spreader (not shown) via a top surface of the package. Thus, the conventional LSI chip 10 radiates heat only from the substrate 11's surface side, as shown in FIG. 8, and does not radiate the heat from the bumps 18 side.
Other prior art relating to the heat radiation include, for example, Japanese Patent Applications Nos. 2002-11902, 2000-323525, and 2003-17494.
The heating value has recently increased with a higher operational frequency of the transistor and higher density mounting. In general, as the temperature of a CMOS transistor rises, the mobility of electrons (holes) in a channel lowers and the performance of the CMOS transistor degrades. On the other hand, the substrate is too thick to improve the heat radiation efficiency. In particular, in the SOI technology, the heat radiation by the self-heating substrate is insufficient. In addition, a Low-k interlayer film material, such as SiLK, which is used to reduce the wiring parasitic capacity, contains air bubbles in its inside, and exhibits poor heat conductions. As a result, as shown in FIG. 8, the heat exhausts near the transistor become insufficient.